a) I've recently seen some attractive synodontis (gold body, dark brown spots, sharply sail-like dorsal.) They aren't multipunctatis but similar in some ways. They do grow up to 29cm, though - that's 11.5 inches - looked them up in pictorial atlas, but it was at the store and I got distracted and didn't write down their name, sorry. How big a tank did you have in mind? These would work, though, if your planned tank was big enough, and make an attractive contrast to your blue haps.

b) re: the "koi pond" - that's nice. All of the pictures are nice, by the way. I suggest the shubunkin goldfish - especially the variety with a mostly white body and red "cap" - they look very koi-like. They don't have the thick, distorted body shape of many fancy varieties.